JargonFile/entries/death code.txt

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2014-04-26 10:52:28 -04:00
death code
2014-04-26 11:54:15 -04:00
n. A routine whose job is to set everything in the computer registers,
memory, flags, everything to zero, including that portion of memory where it
is running; its last act is to stomp on its own store zero instruction.
Death code isn't very useful, but writing it is an interesting hacking
challenge on architectures where the instruction set makes it possible, such
as the PDP-8 (it has also been done on the DG Nova). Perhaps the ultimate
death code is on the TI 990 series, where all registers are actually in RAM,
and the instruction store immediate 0 has the opcode 0. The PC will
immediately wrap around core as many times as it can until a user hits HALT.
Any empty memory location is death code. Worse, the manufacturer recommended
use of this instruction in startup code (which would be in ROM and therefore
survive).